Area Forecast Discussion
Issued by NWS Charleston, WV

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000
FXUS61 KRLX 212006
AFDRLX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
306 PM EST SUN DEC 21 2014

.SYNOPSIS...
WEAK HIGH PRESSURE EXITS THIS EVENING.  SYSTEM CLIPS THE MOUNTAINS
MONDAY. STRONG LOW PRESSURE SYSTEM LIFTS NORTHEAST ACROSS THE OHIO
VALLEY THROUGH CHRISTMAS EVE.

&&

.NEAR TERM /THROUGH MONDAY/...
HIGH PRESSURE AND LIGHT E FLOW HAD MANAGED TO ERADICATE THE STRATUS
ALONG AND E OF THE OHIO RIVER TODAY.  THIS HAS ALLOWED FOR DAYTIME
HEATING BUT WILL ALSO ALLOW FOR RADIATIVE COOLING THIS EVENING.

A WARM WAVE RIDES UP THE SE COAST LATE TONIGHT AND MON.  THE
QUESTION IS TO WHAT DEGREE THIS FLAT WAVE CAN THROUGH PRECIPITATION
BACK INTO THE FCST AREA...AND WHEN WILL SUCH PRECIPITATION REACH THE
GROUND GIVEN THE DRY MID LEVEL AIR TO START OUT WITH.

MOST OF THE GUIDANCE SUGGESTS TEMPERATURES NEAR OR JUST BELOW
FREEZING IN THE NRN WV MOUNTAINS...MAINLY ON THE HIGHER PEAKS AND
DOWN THE ERN SLOPES INTO THE GREENBRIER VALLEY.  MODELS DEPICT A
WARM LAYER ALOFT WITH TEMPERATURES 1-2C IN THE H925-H85 LAYER.  THIS
SUGGESTS MELTING OF SNOW WHICH MEANS THERE COULD BE SLEET AND SNOW
MIXED IN WITH ANY FREEZING RAIN.  TEMPERATURES IN CLOUD SUPPORTIVE
OF ICE CRYSTALS ARE LOST EARLY ON AS THE MOIST LAYER BECOMES MORE
SHALLOW.  THIS WOULD TEND THE PRECIPITATION BACK TOWARD FREEZING
RAIN OR FREEZING DRIZZLE.

THIS LEAVES THE TIMING OF THE ARRIVAL OF PRECIPITATION CRUCIAL AS
TEMPERATURES SLOWLY CLIMB ABOVE FREEZING IN THE GREENBRIER VALLEY.
CURRENT GRID DEPICTION IS FOR POPS CLIMBING ABOVE 50 YIELDING
MEASURABLE QPF AS TEMPERATURES CLIMB.  THIS LIMITS ICE ACCRETION TO
AT MOST A HUNDREDTH AND NOT VERY WIDESPREAD.  THE SREF DOES
INTERSECT HIGH POPS WITH POCKETS OF HIGH PROBABILITIES FOR SFC
TEMPERATURES AT OR BELOW FREEZING MON MIDDAY INTO THE AFTERNOON.
COORD WITH WPC/WWD-PBZ-LWX-RNK ON ISSUANCE ADV FOR FREEZING RAIN
POCAHONTAS COUNTY 11-17Z.

THE REMAINDER OF THE FCST AREA SEES A RETURN OF CLOUD COVER
TONIGHT...SETTING THE STAGE FOR ANOTHER GREY DECEMBER DAY...ALTHOUGH
THE CLOUDS DO DECREASE BEHIND THE SYSTEM MON AFTERNOON.

USED NEAR TERM...IN PARTICULARLY THE WRFNMM...RUC AND THE HRRR FOR
TEMPERATURES TONIGHT AND NAM-BASED VALUES FOR THOSE ON MON...WHICH
SHOULD FEATURE A MILDER AFTERNOON.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
5H TROUGH TO DIG OVER THE MIDWEST WITH SEVERAL WAVES RIDING NWD
ALONG THE COAST OF SE US. THIS LEAVES OUR CWA IN THE WARM SECTOR
OF BAROCLINIC FORCING THAT WILL BE TAKING PLACE IN VARIOUS PHASES
THROUGHOUT THE PERIOD. FIRST WEAKER WAVE DEFTLY EXITS TO THE EAST
BY TUESDAY MORNING AND ONLY BROUGHT ISOLD AND LOW CHANCE POPS TO
THE EASTERN MOUNTAINS. WAA WILL BE FULL SWING UNDER SOUTH TO
SOUTHWEST FLOW AND CHANCES FOR ANY PRECIPITATION OF THE FROZEN
VARIETY WILL BE NIL.

A SECOND STRONGER WAVE WILL PUSH NORTH TUESDAY NIGHT AND
WEDNESDAY. MODELS STILL SHOW POOR PHASING BETWEEN NORTHERN AND
SOUTH STREAM SYSTEMS WITH MAIN SFC LOW DEVELOPMENT OCCURRING NORTH
OF THE GREAT LAKES. THIS DELAYS FROPA AND ONSET OF CAA AND PLACES
CWA SQUARELY IN THE WARM SECTOR THROUGH WEDNESDAY. FRONT WILL
FINIALLY PUSH THROUGH WEDNESDAY NIGHT WITH PRECIPITATION COMING TO
AN END...MOSTLY BEFORE THE COLDER AIR ON BACKSIDE IS ABLE TO MOVE
IN. THUS...ONLY HAVE VERY LIGHT SNOW AMOUNTS FIGURED FOR THE
MOUNTAINS IN NORTHEASTERN COUNTIES.

USED MAINLY SREF FOR TIMING ONSET OF PRECIP DEVELOPMENT. FOR
TEMPS...USED BC GRIDS WITH A BLEND TOWARD INHERITED FORECAST
TEMPS.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
COLD FRONT TO THE EAST OF THE CWA AT THE BEGINNING OF THE
PERIOD...WITH A GRADUAL CHANGE OVER TO SNOW FOR CHRISTMAS EVE NIGHT
AND CHRISTMAS DAY. AT THIS POINT...REALLY NOT EXPECTING MUCH IN
TERMS OF SNOWFALL ACCUMULATIONS. WINDS HOWEVER ON THURSDAY ARE STILL
EXPECTED TO BE GUSTY POST FRONTAL.

AREA DRIES OUT THURSDAY EVENING AS THE LOW PULLS OFF TO THE
NORTHEAST. HIGH PRESSURE THEN BRIEFLY BUILDS IN FOR A BREAK IN
PRECIPITATION. ANOTHER COLD FRONT WILL DROP ACROSS THE AREA OVER THE
WEEKEND...CREATING A CHANCE FOR LIGHT SNOW SHOWERS...AND WILL USHER
IN MUCH COLDER AIR INTO THE REGION. TRENDED TEMPERATURES NEXT
WEEKEND DOWN FROM PREVIOUS FORECAST.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
LIGHT E FLOW ON S SIDE OF HIGH PRESSURE HAD FINALLY ERADICATED THE
MVFR TO HIGH IFR STRATOCU...WITH ALL SITES VFR TO START THE FCST.
THIS WILL HOLD THROUGH SUNSET.

A WEAK WAVE OF LOW PRESSURE MOVES UP ALONG THE SE COAST OVERNIGHT
TONIGHT AND MON.  THIS WILL SPILL CLOUDS BACK INTO THE AREA
OVERNIGHT...WITH RAIN LIKELY IN THE MOUNTAINS...MAINLY ON THE
EASTERN SLOPES...WHERE SNOW...SLEET AND FREEZING RAIN ARE LIKELY TO
BE MIXED IN THROUGH THE MORNING HOURS.

MVFR TO HIGH IFR STRATOCU SHOULD RETURN TO BKW TONIGHT...WITH A MORE
WIDESPREAD MVFR DECK DEVELOPING BY MON MORNING.  CLOUD HEIGHTS
SHOULD INCREASE MON AFTERNOON AS CLOUD AMOUNT LOWERS.

LIGHT AND VARIABLE TO E SFC FLOW WILL BECOME LIGHT SE TONIGHT AND
REMAIN SO ON MON.  SE WINDS WILL BECOME A BIT GUSTY ON THE RIDGES
INCLUDING BKW OVERNIGHT INTO MON.  FLOW ALOFT WILL REMAIN LIGHT S TO
SW.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z MONDAY...

FORECAST CONFIDENCE: MEDIUM.

ALTERNATE SCENARIOS: TIMING AND LOCATION OF A MVFR STRATUS DECK
COULD VARY CONSIDERABLY OVERNIGHT INTO MON.

EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH:   TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW:    TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.

UTC 1HRLY       20   21   22   23   00   01   02   03   04   05   06   07
EST 1HRLY       15   16   17   18   19   20   21   22   23   00   01   02
CRW CONSISTENCY  M    M    H    H    H    H    H    H    H    H    H    H
HTS CONSISTENCY  M    M    H    H    H    H    H    H    H    H    H    H
BKW CONSISTENCY  H    H    H    M    M    M    M    M    L    L    L    L
EKN CONSISTENCY  H    H    H    H    H    H    H    H    H    H    H    H
PKB CONSISTENCY  M    M    M    M    M    H    H    H    H    H    H    H
CKB CONSISTENCY  M    M    M    M    H    H    H    H    H    H    H    H

AFTER 18Z MONDAY...
IFR POSSIBLE IN MOUNTAINS INTO MON AFTERNOON IN A WINTRY MIX. IFR
POSSIBLE IN RAIN TUE NT INTO WED...CHANGING TO SNOW SHOWERS WED
NT...AS AN INTENSE LOW PRESSURE CENTER PASSES.

&&

.RLX WATCHES/WARNINGS/ADVISORIES...
WV...FREEZING RAIN ADVISORY FROM 6 AM TO NOON EST MONDAY FOR WVZ046.
OH...NONE.
KY...NONE.
VA...NONE.

&&

$$
SYNOPSIS...TRM/RPY/SL/30
NEAR TERM...TRM
SHORT TERM...KMC
LONG TERM...SL
AVIATION...TRM








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